Therapeutic agents may be delivered to a targeted location in a human utilizing a number of different methods. For example, agents may be delivered nasally, transdermally, intravenously, orally, or via other conventional methods. Delivery may vary by release rate (e.g., quick release, slow release, or biphasic release). Delivery may also vary as to how the drug is administered. Specifically, a drug may be administered locally to a targeted area, or administered systemically.
With systemic administration, the therapeutic agent is administered in one of a number of different ways including orally, inhallationally, or intravenously to be systemically processed by the patient. However, there are drawbacks to systemic delivery of a therapeutic agent, one of which is that high concentrations of the therapeutic agent travels to all portions of the patient's body and can have undesired effects at areas not targeted for treatment by the therapeutic agent. Furthermore, large doses of the therapeutic agent only amplify the undesired effects at non-target areas. As a result, the amount of therapeutic agent that results in application to a specific targeted location in a patient may have to be reduced when administered systemically to reduce complications from toxicity resulting from a higher dosage of the therapeutic agent.
An alternative to the systemic administration of a therapeutic agent is the use of a targeted local therapeutic agent delivery approach. With local delivery of a therapeutic agent, the therapeutic agent is administered using a medical device or apparatus, directly by hand, or sprayed on the tissue, at a selected targeted tissue location of the patient that requires treatment. The therapeutic agent emits, or is otherwise delivered, from the medical device apparatus, and/or carrier, and is applied to the targeted tissue location. The local delivery of a therapeutic agent enables a more concentrated and higher quantity of therapeutic agent to be delivered directly at the targeted tissue location, minimizing or eliminating broader systemic side effects. With local delivery, the therapeutic agent that escapes the targeted tissue location dilutes as it travels to the remainder of the patient's body, substantially reducing or eliminating systemic effects.
Local delivery is often carried out using a medical device as the delivery vehicle. One example of a medical device that is used as a delivery vehicle is a stent. Boston Scientific Corporation sells the Taxus® stent, which contains a polymeric coating for delivering Paclitaxel. Johnson & Johnson, Inc. sells the Cypher® stent which includes a polymeric coating for delivery of Sirolimus.
Targeted local therapeutic agent delivery using a medical device can be further broken into two categories, namely, short term and long term. The short term delivery of a therapeutic agent occurs generally within a matter of seconds or minutes to a few days or weeks. The long term delivery of a therapeutic agent occurs generally within several weeks to a number of months. Typically, to achieve the long term delivery of a therapeutic agent, the therapeutic agent must be combined with a delivery agent, or otherwise formed with a physical impediment as a part of the medical device, to slow the release of the therapeutic agent.
What is desired is a coated medical device wherein the coating is applied in a manner that provides a uniform consistent coating. The coating can be a bio-absorbable delivery agent having non-inflammatory characteristics that is able to be prepared in combination with at least one therapeutic agent for the delivery of that therapeutic agent to body tissue in a controlled release manner.
In applying coatings to medical devices, such as stents and catheters, coverage and uniformity are important factors in the getting optimal performance out of the coated medical device. If a device does not have proper coverage then there may be areas on the device that do not have proper coating which can lead to all the problems typically associated with uncoated devices. Similar problems can arise when the coating is not uniform. Non-uniform coatings can cause inconsistent interactions, especially when a therapeutic agent is being delivered. Ideally, the coating should be uniform over the medical device so that dosage and interaction with tissue can be better controlled.